The present invention relates to a system for controlling the voltage to be applied to glow plugs which are installed in an engine, especially a diesel engine.
In the diesel engine, just before the engine is started, a voltage is applied to the glow plugs for preheating the same. And after the engine is started, mainly during the warm-up period, a voltage is also applied to the glow plugs (which is called after glow) for preventing the vibrations and noise from occurring in the engine and reducing white smoke within the exhaust gases.
But, during the warm-up period, such a high voltage as to be required during the preheating period need not be applied to the glow plugs.
In particular, since heating elements of which rated voltage is smaller than the battery voltage are recently employed as the glow plugs in order to effect the preheating operation rapidly, excess voltage is applied to the glow plugs during the after glow period. As a result, the life of the glow plugs is decreased.
The amount of heat which is required to be generated by the glow plugs during the after glow period is related to the engine temperature.
When the engine is started, the temperature of engine rises. Due to the rise of engine temperature, the glow plugs also receive heat from the engine. Therefore, it is desirable to change the voltage to be applied to the glow plugs in accordance with the engine temperature during the after glow period.
Normally, one battery is mounted on a vehicle so that the voltage applied to the glow plugs is constant. Therefore, a voltage dropping means is required for dropping the voltage to be applied to the glow plugs during the after glow period.
Conventionally, it has been proposed to provide resistors in an electric path between the battery and the glow plugs. However, according to this conventional means, thermal loss occurs and a special structure is required in order to arrange the resistors which generates heat.
Accordingly, one object of the present invention is to provide an after glow control system for an engine, which can reduce the voltage to be applied to the glow plugs without thermal loss.
Another object of the present invention is to provide an after glow control system for an engine which can change the voltage to be applied to the glow plugs in accordance with the engine temperature during the after glow period.